Centralizer for wireline tool

Abstract

A centralizer assembly replaces an existing centralizer of a wireline tool so the tool can be used with smaller casing, such as casing smaller than 6-in. The assembly includes first and second centralizer units that replace the existing centralizer on a mandrel. Each unit has a sleeve that fits in a recess of the mandrel, and each unit has slider blocks disposed together in the recess on opposing sides of a divider on the sleeve. Arms hingedly connected to the blocks on each unit connect together at a joint having a roller for engaging in the casing. On each unit, a common pin is disposed through the slider blocks, and biasing elements on the common pin bias the blocks toward one another with different amounts of bias.

Claims

1. An assembly for converting a given centralizer of a wireline tool for use with smaller diameter casing, the wireline tool having a mandrel with first and second recesses separated by an upset, the given centralizer having first and second slider blocks disposed respectively in the first and second recesses and having a plurality of given radial supports, each of the given radial supports having a first arm hingedly connected to the first slider block, each of the radial supports having a second arm hingedly connected to the second slider block and hingedly connected to the first arm, the assembly comprising: first and second centralizers replacing the given centralizer on the mandrel, the first centralizer having a first divider disposed in the first recess and having third and fourth slider blocks disposed together in the first recess on respective sides of the first divider, the first centralizer having a third arm hingedly connected to the third slider block, the first centralizer having a fourth arm hingedly connected to the fourth slider block and hingedly connected to the third arm; and the second centralizer having a second divider disposed in the second recess and having fifth and sixth slider blocks disposed together in the second recess on respective sides of the second divider, the second centralizer having a fifth arm hingedly connected to the fifth slider block, the second centralizer having a sixth arm hingedly connected to the sixth slider block and hingedly connected to the fifth arm.

2. The assembly of claim 1, wherein each of the respective slider blocks comprises at least two pieces fitting together in the respective recess around the mandrel.

3. The assembly of claim 1, wherein each of the first and second dividers comprises a sleeve disposed in the respective recess, the sleeve having a shoulder for the respective divider and having the respective slider blocks disposed on the sleeve on opposing sides of the shoulder.

4. The assembly of claim 3, wherein each of the sleeves comprises at least two pieces fitting together in the respective recess around the mandrel.

5. The assembly of claim 1, wherein each of the respective slider blocks for the first and second centralizers comprises a common pin disposed through adjacent shoulders on the respective slider blocks, the common pin having a first shoulder end and having a first biasing element disposed on the common pin between the first shoulder end and a first of the adjacent shoulders, the common pin having a second shoulder end and having a second biasing element disposed on the common pin between the second shoulder end and a second of the adjacent shoulders.

6. The assembly of claim 5, wherein the first biasing element comprises a first stiffnesses; and wherein the second biasing element comprises a second stiffness different from the first stiffness.

7. The assembly of claim 5, wherein a first shouldering distance between the first end of the common pin and the first adjacent shoulder is greater than a second shouldering distance between the second end of the common pin and the second adjacent shoulder.

8. The assembly of claim 1, wherein the first centralizer comprises a plurality of first radial supports, each of the first radial supports having a set of the third and fourth arms; and wherein the second centralizer comprises a plurality of second radial supports, each of the second radial supports having a set of the fifth and sixth arms.

9. The assembly of claim 8, wherein the first radial supports are arranged about the third and fourth slider blocks alternatingly closer to edges of the third and fourth slider blocks.

10. A centralizer for use on a wireline tool in casing having a number of inner diameters, the wireline tool having a mandrel with a dividing upset, the centralizer comprising: a first slider block disposed on the mandrel on a first side of the dividing upset; a second slider block disposed on the mandrel on a second side of the dividing upset, the first and second slider blocks being separable from one another; a first arm hingedly connected to the first slider block; a second arm hingedly connected to the second slider block and hingedly connected to the first arm; a common pin disposed between the first and second slider blocks; a first biasing element arranged between the common pin and at least one of the first and second slider blocks; and a second biasing element arranged between the common pin and at least one of the first and second slider blocks, the first biasing element being configured to bias the common pin and the at least one of the first and second slider blocks for an initial extent of separation between the first and second slider bocks, the second biasing element being configured to bias the common pin and the at least one of the first and second slider blocks for a subsequent extent of the separation between the first and second slider bocks.

11. The centralizer of claim 10, wherein the first slider block comprises a first shoulder facing away from the dividing upset; wherein the second slider block comprises a second shoulder facing away from the dividing upset; wherein the common pin is disposed through the first and second shoulders on the respective slider blocks, the common pin having third and fourth shoulders; wherein the first biasing element is disposed on the common pin between the first shoulder of the first slider block and the third shoulder of the common pin; and wherein the second biasing element is disposed on the common pin between the second shoulder of the second slider block and the fourth shoulder end of the common pin.

12. The centralizer of claim 11, wherein the first biasing element comprises a first stiffnesses; and wherein the second biasing element comprises a second stiffness different from the first stiffness.

13. The centralizer of claim 11, wherein a first shouldering distance between the first shoulder of the first slider block and the third shoulder of the common pin is greater than a second shouldering distance between the second shoulder of the second slider block and the fourth shoulder of the common pin.

14. The centralizer of claim 10, wherein the first biasing element comprises a first stiffnesses, and the second biasing element comprises a second stiffness different from the first stiffness; and/or wherein the initial extent is shorter than the subsequent extent.

15. The centralizer of claim 10, wherein the centralizer comprises a plurality of first radial supports, each of the radial supports having a set of the first and second arms.

16. The centralizer of claim 10, wherein the first slider block comprises a first shoulder facing away from the dividing upset; wherein the common pin is connected from the second slider block and is disposed through the first shoulder on the first slider block, the common pin having a second shoulder; wherein the first biasing element is disposed on the common pin between the first shoulder of the first slider block and the second biasing element; and wherein the second biasing element is disposed on the common pin between the second shoulder of the common pin and the first biasing element.

17. A centralizer for use on a wireline tool in casing having a number of inner diameters, the wireline tool having a mandrel, the centralizer comprising: a sleeve disposed on the mandrel, the sleeve having a dividing upset; a first slider block disposed on the sleeve on a first side of the dividing upset; a second slider block disposed on the sleeve on a second side of the dividing upset, the first and second slider blocks being separable from one another; a first arm hingedly connected to the first slider block; a second arm hingedly connected to the second slider block and hingedly connected to the first arm; a first biasing element arranged between the first and second slider blocks; and a second biasing element arranged between the first and second slider blocks, the first biasing element biasing an initial extent of separation between the first and second slider bocks, the second biasing element biasing a subsequent extent of the separation between the first and second slider bocks.

18. The centralizer of claim 17, wherein the first slider block comprises a first shoulder facing away from the dividing upset; wherein the second slider block comprises a second shoulder facing away from the dividing upset; wherein the centralizer comprises a common pin disposed through the first and second shoulders on the respective slider blocks, the common pin having third and fourth shoulders; wherein the first biasing element is disposed on the common pin between the first shoulder of the first slider block and the third shoulder of the common pin; and wherein the second biasing element is disposed on the common pin between the second shoulder of the second slider block and the fourth shoulder end of the common pin.

19. The centralizer of claim 18, wherein a first shouldering distance between the first shoulder of the first slider block and the third shoulder of the common pin is greater than a second shouldering distance between the second shoulder of the second slider block and the fourth shoulder of the common pin.

20. The centralizer of claim 17, wherein the first biasing element comprises a first stiffnesses, and the second biasing element comprises a second stiffness different from the first stiffness; and/or wherein the initial extent is shorter than the subsequent extent.

21. The centralizer of claim 17, wherein the centralizer comprises a plurality of first radial supports, each of the radial supports having a set of the first and second arms.

22. The centralizer of claim 17, wherein the first slider block comprises a first shoulder facing away from the dividing upset; wherein the centralizer comprises a common pin connected from the second slider block and disposed through the first shoulder on the first slider block, the common pin having a second shoulder; wherein the first biasing element is disposed on the common pin between the first shoulder of the first slider block and the second biasing element; and wherein the second biasing element is disposed on the common pin between the second shoulder of the common pin and the first biasing element.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 illustrates an elevational view of a portion of a wireline tool having a conventional roller centralizer of the prior art.

(2) FIGS. 2A-2B illustrate sectioned views of the conventional roller centralizer of the prior art in stages of movement.

(3) FIG. 3 diagrams a sonde on a wireline tool at different decentralized orientations relative to surrounding casing.

(4) FIG. 4 graphs eccentricity of the conventional roller centralizer as a function of inner casing diameters relative to radial arm play.

(5) FIGS. 5A-5C illustrate elevational views of a portion of a wireline tool having a conventional roller centralizer of the prior art being replaced with a centralizer assembly of the present disclosure.

(6) FIGS. 6A-6B illustrate sectioned views of one of the centralizers of the disclosed assembly in stages of movement.

(7) FIG. 7A graphs eccentricity of the disclosed centralizer as a function of inner casing diameters relative to radial arm play.

(8) FIG. 7B graphs insertion force relative to the arm angle of the disclosed centralizer.

(9) FIG. 8A illustrates schematic views of one biasing arrangement for the disclosed centralizer during operation.

(10) FIG. 8B illustrates schematic views of another biasing arrangement for the disclosed centralizer during operation.

(11) FIGS. 9A-9B illustrate elevational views of the centralizers of the present disclosure, revealing features of their biasing elements.

(12) FIGS. 10A-10B illustrate sectioned views of one of the disclosed centralizers of the present disclosure, revealing additional features of the biasing elements in different stages of movement.

(13) FIGS. 11A-11B illustrate sectioned views of the disclosed centralizer in a biased state.

(14) FIGS. 12A-12B illustrate sectioned views of the disclosed centralizer in another biased state.

(15) FIG. 13A graphs spring force relative to inner casing diameters for a conventional type of biasing arrangement of a prior art roller centralizer.

(16) FIG. 13B graphs centralizing force relative to inner casing diameters for the conventional type of biasing arrangement.

(17) FIG. 14A graphs spring force relative to inner casing diameters for the disclosed biasing arrangement.

(18) FIG. 14B graphs centralizing force relative to inner casing diameters for the disclosed biasing arrangement.

DETAILED DESCRIPTION OF THE DISCLOSURE

(19) FIGS. 5A-5C illustrate elevational views of a portion of a wireline tool 10 having a conventional roller centralizer 20 of the prior art being replaced with a conversion centralizer assembly 40 of the present disclosure. In particular, the conversion centralizer assembly 40 shown in FIGS. 5B-5C is used for replacing components of the centralizer 20 of the wireline tool 10 shown in FIG. 5A so the tool 10 can be used with smaller diameter casing.

(20) As noted above and shown again in FIG. 5A, the wireline tool 10 has the tool body 12 from which the existing centralizer 20 and sonde 14 extend. The centralizer 20 has the mandrel 22 connected at one end to the tool body 12, and the mandrel 22 supports the sonde 14 from its distal end. The mandrel 22 has the first and second recesses 26a-b separated by an upset having shoulders (25a-b).

(21) The first and second slider blocks 32a-b of the conventional centralizer 20 are disposed respectively in the first and second recesses 26a-b, and the blocks 32a-b have a plurality of radial supports 30 interconnecting them. Each of the radial supports 30 has a first arm 36a hingedly connected at hinged connection 38a to the first slider block 32a, and each of the radial supports 30 has a second arm 36b hingedly connected at hinged connection 38b to the second slider block 32b and hingedly connected to the first arm 36a at a hinged connection 38c.

(22) The conversion assembly 40 includes first and second centralizers 50a-b that replace the existing centralizer 20 on the mandrel 22. In converting the arrangement, the standard centralizer components are removed from the mandrel 22, and the two small casing centralizers 50a-b are installed completely within the slider block recesses 26a-b of the mandrel 22 to address the root problem of tool eccentricity. In general and as described below, the small casing centralizers 50a-b have small centralizer arms and compact form factors.

(23) As shown in FIG. 5B, the first centralizer 50a has a first divider 52a disposed in the first recess 26a and has two slider blocks 54a-b disposed together in the first recess 26a on respective sides of the first divider 52a. The second centralizer 50b similarly has a second divider 52b disposed in the second recess 26b and has two slider blocks 54a-b disposed together in the second recess 26b on respective sides of the second divider 52b.

(24) As shown in FIG. 5B for assembly purposes, each of the respective slider blocks 54a-b can include at least two pieces or halves fitting together in the respective recess 26a-b around the mandrel 22. Additionally, each of the first and second dividers 52a-b can include a sleeve 53a-b disposed in the respective recess 26a-b, with the sleeve 53a-b having a shoulder for the respective divider 52a-b and having the respective slider blocks 54a-b disposed on the sleeve 53a-b on opposing sides of the shoulder 52a-b. For assembly purposes, each of the sleeves 53a-b can include at least two pieces or halves fitting together in the respective recess 26a-b around the mandrel 22.

(25) To do the conversion, for example, a set of sleeves 53a-b with the dividers or shoulders 52a-b integral to the sleeves 53a-b are installed onto the mandrel 22 in the recess 26a-b designed for the conventional centralizer (20). The blocks 54a-b for the two small form centralizers 50a-b are then installed where the single, larger centralizer blocks were previously installed.

(26) For each centralizer 50a-b, a plurality of radial supports 56 are disposed between the slider blocks 54a-b around the mandrel 22. As shown in FIG. 5C, the supports 56 each include a first arm 57a hingedly connected to a first of the slider blocks 54a and include a second arm 57b hingedly connected to a second of the slider blocks 54b. The two arms 57a-b have their distal ends hingedly connected together at a joint, which has a roller.

(27) With the centralizers 50a-b of the assembly 40 installed as shown in FIG. 5C in place of the conventional centralizer (20; FIG. 5A), the two centralizers 50a-b act to centralize the mandrel 22 and connected sonde 14 in smaller casing diameters without the considerable effective radial play (linkage slop) found in existing roller centralizers.

(28) FIGS. 6A-6B illustrate sectioned views of one of the disclosed centralizers 50b in stages of movement, including insertion I into smaller diameter casing 16. Here, the distal centralizer 50b (i.e., the one near the sonde 14 on the distal end of the mandrel 22) is depicted. As shown in FIG. 6A, the slider blocks 54a-b with the centralizer 50b unrestricted can both shoulder against the divider 52b of the sleeve 53b in the recess 26b. When the distal arms 57b engage the casing 16, the distal block 54b as depicted in the detail stays shouldered against the divider 52b. A biasing arrangement, which is not shown here but is disclosed below, spaces out the proximal slider block 54a, which has an allowable travel T dictated by the sleeve/recess 53b/26b.

(29) As shown, the intermediate hinged connection or joint 58c between the respective arms 57a-b includes a roller 59. Eventually on insertion as shown in FIG. 6B, the arms 56a-b retract inward as the proximal slider block 54a reaches the end of stroke, and the rollers 59 on the connected ends of the arms 56a-b engage inside the casing 16. The shouldering of the distal block 54b on the divider 52b ensures the proximal block 54a has adequate travel allowance for the maximum operating range of the centralizer 50b. (As will be appreciated, the centralizer 50b must also have adequate block travel in both proximal and distal locations to prevent getting stuck. Moreover, the proximal centralizer 50a of the assembly 40 can be comparably configured and arranged.)

(30) In one example, the length for the recess 26b as modified by the sleeve 53b can be about 10.75-in. The small casing centralizer 50b can fully collapse into casing 16 having an inner diameter of 4.5-in with additional clearance available. The arm angles can be limited to 15° at a 4-in inner casing diameter, and the radial arm play at the 4-in inner casing diameter can be reduced by 87%. (Again, the proximal centralizer 50a of the assembly 40 can be comparably configured and arranged.)

(31) For example, FIG. 7A graphs eccentricity of a disclosed centralizer (50a-b) as a function of inner casing diameters relative to radial arm play. Radial arm play for an inner casing diameter of 6.5-in may be well less than 0.05 in, and the radial arm play may only increase to about 0.05-in for an inner casing diameter of 4-in. For some wireline tools, the eccentricity has a preferred limit, such as a limit of 1% eccentricity of the inner casing diameter depicted by the dashed line in the graph. As can be seen, the eccentricity from the radial arm play does not exceed the preferred limit until the inner casing diameter reaches as low as 4-in.

(32) In addition, the insertion force required to insert the centralizer (50a-b) can be reduced. For example, FIG. 7B graphs insertion force relative to the arm angle on the disclosed centralizer (50a-b). The insertion force of the centralizer (50a-b) can be reduced to below 120-lbf, which is a reduction of more than 90% from the insertion force required of the conventional roller centralizer.

(33) To further address the centralizing force profile over the range of casing sizes, a biasing arrangement of the disclosed centralizer 50a-b houses biasing elements between the slider blocks 52a-b. In particular, FIGS. 8A-8B illustrate schematic views of biasing arrangements for the disclosed centralizer (50a-b) during operation.

(34) In FIG. 8A, the two slider blocks 54a-b of one of the centralizers (50a-b) are disposed adjacent one another. (Arms of the radial supports are not shown between the blocks 54a-b for simplicity.) One (e.g., distal) slider block 54b has a pin 62 connected thereto, which passes to the other (proximal) slider block 54a. First and second biasing elements 60a-b are stacked in series on the pin 62 between a pin shoulder 64 and a block shoulder 55.

(35) As noted, engagement of the arms (not shown) with the casing wall urges or pushes the blocks apart relative to any dividing upset. In general, one of the biasing elements (e.g., 60a) biases an initial extent of separation between the first and second slider blocks 54a-b, while the other biasing element (e.g., 60b) biases a subsequent extent of the separation between the first and second slider blocks 54a-b. For example, one of the biasing elements (e.g., 60a) has a lighter/heavier stiffness than the other biasing element (60b), and/or one of the biasing elements (e.g., 60a) has a longer/shorter travel distance than the other biasing element (60b).

(36) With separation of the slider blocks 54a-b, for instance, the first biasing element 60a biases the initial extent of the separation until the biasing element 60a shoulders or reaches stack length, as shown in the intermediate state. With further separation of the slider blocks 54a-b, the second biasing element 60b then biases the subsequent extent of the separation until the second biasing element 60b shoulders or reaches stack length, as shown in the final state.

(37) In the arrangement of FIG. 8B, a common pin 62 passes through the adjacent slider blocks 54a-b. A first biasing elements 60a is stacked on the pin 62 between a first pin shoulder 64a and a first block shoulder 55a. A second biasing elements 60b is stacked on the pin 62 between a second pin shoulder 64b and a second block shoulder 55b.

(38) In general, one of the biasing elements (e.g., 60a) biases an initial extent of separation between the first and second slider blocks 54a-b, while the other biasing element (e.g., 60b) biases a subsequent extent of the separation between the first and second slider blocks 54a-b. For example, one of the biasing elements (e.g., 60a) has a lighter/heavier stiffness than the other biasing element (60b), and/or one of the biasing elements (e.g., 60a) has a longer/shorter travel distance than the other biasing element (60b).

(39) With separation of the slider blocks 54a-b, for instance, the first biasing element 60a biases the initial extent of the separation until the biasing element 60a shoulders or reaches stack length, as shown in the intermediate state. With further separation of the slider blocks 54a-b, the second biasing element 60b then biases the subsequent extent of the separation until the second biasing element 60b shoulders or reaches stack length, as shown in the final state.

(40) Using the second biasing arrangement disclosed above with reference to FIG. 8B, FIGS. 9A-9B illustrate elevational views of the centralizers 50a-b of the present disclosure, revealing features of biasing elements or springs 60a-b used with the slider blocks 54a-b. The centralizers 50a-b are each arranged with the proximal slider block 54a having a first biasing element 60a and with the distal slider block 54b having a second biasing element 60b on the common pin 62. Thus, the biasing arrangement is the same for both centralizers 50a-b on the mandrel 22, but other configurations could be used.

(41) As also shown in FIGS. 9A-9B, the centralizers 50a-b each preferably has a plurality of radial supports 56 disposed about the slider blocks 54a-b. The radial supports 56 are arranged about the slider blocks 54a-b in an alternating and opposing pattern. For example, the first arm 57a of one support 56a is connected closer to the outer edge of the proximal slider block 54a, whereas the second arm 57b of the support 56a is connected closer to the inner edge of the distal slider block 54b. The adjacent support 56b is arranged in opposing relation. Namely, the first arm 57a is connected closer to the inner edge of the proximal slider block 54a, whereas the second arm 57b is connected closer to the outer edge of the distal slider block 54b. The first and second arms 57a-b may have the same or different lengths. This pattern is repeated uniformly about the slider blocks 54a-b such that there are a plurality of alternating supports 56a-d disposed about the mandrel 22. As shown here, four supports 56a-d may be provided, and the two centralizers 50a-b may be comparably arranged.

(42) FIGS. 10A-10B, 11A-11B, and 12A-12B illustrate sections views of one of the disclosed centralizer 50 of the present disclosure, revealing additional features of the biasing elements or springs 60a-b in different stages of movement. Here, the centralizer 50 depicted is the distal centralizer 50b closer to the sonde (14).

(43) As shown in FIGS. 10A-10B, the respective slider blocks 54a-b for the centralizer 50b include a common pin or guide rod 62 disposed through adjacent shoulders 55a-b on the respective slider blocks 54a-b. The common pin 60 has a first (proximal) shoulder end 64a and has a first biasing element 60a disposed on the common pin 62 between the first shoulder end 64a and a first of the adjacent shoulders 55a. The common pin 62 also has a second (distal) shoulder end 64b and has a second biasing element 60b disposed on the common pin 62 between the second shoulder end 64b and a second of the adjacent shoulders 55b.

(44) The first biasing element 60a has a first stiffnesses, and the second biasing element 60b has a second stiffness different from the first stiffness. For this distal centralizer 50b, the proximal biasing element 60a is a heavy spring, and the distal biasing elements 60b is a light spring with less stiffness.

(45) Additionally, a first shouldering distance D.sub.a between the proximal end 64a of the common pin 60a and the first adjacent shoulder 55a (for the heavy spring 60a) is greater than a second shouldering distance D.sub.b between the distal end 64b of the common pin 62 and the second adjacent shoulder 55b (for the light spring 60b). As will be appreciated, the respective spring 60a-b may have a stack length less than the shouldering distance. This is true, for example, with the heavy spring 60a.

(46) When the centralizer 50b is unengaged as shown in FIGS. 10A-10B, the biasing elements 60a-b on the common pin 62 bring the slider blocks 54a-b together toward the divider 52b. During engagement of the arms 56a-b with casing (not shown), the biasing elements 60a-b are compressed by the slider blocks 54a-b moving apart from one another through the linkage of the arms 56a-b. FIGS. 11A-11B show the slider blocks 54a-b during a state of moving apart.

(47) When used in larger casing diameters, both biasing elements 60a-b active and result in an effective spring constant that produces an adequate centralizing force. As the angle of the centralizing arms 56a-b becomes smaller when used in small casing, however, the centralizing load becomes smaller so it is desirable to increase the spring stiffness at small casing sizes. This increased spring stiffness at smaller casing sizes is accomplished here using the short shouldering distance D.sub.b between the spring stops 55b, 64b for the second biasing element or light spring 60b.

(48) In particular, FIGS. 12A-12B show the centralizer 50b compressed to an even smaller casing size. As shown, the spring stops 55b, 64b prevent the light spring 60b from compressing further as the short shouldering distance D.sub.b closes. This changes the effective spring rate to the stiffer spring 60a and dramatically increases the centralizing force for the smaller casing range.

(49) As will be appreciated, the proximal centralizer (50a) for the assembly (40) can be comparably arranged and configured as the distal centralizer 50b depicted here. As can be seen, the biasing arrangement uses a two-stage series spring assembly that varies the effective spring constant using two distinct spring constants. The mechanical advantage and spring constants of the disclosed arrangement act to level out the centralizer's side force profile over the entire range of casing sizes in which the centralizer 50a-b is intended for use. This is in direct contrast to the conventional type of biasing arrangement, such as found on a centralizer of the prior art.

(50) For example, FIG. 13A graphs spring force relative to inner casing diameters for a conventional type of biasing arrangement for a centralizer of the prior art. As the centralizer arms are compressed into smaller diameter casing, the conventional spring assembly compresses with increasing spring force. However, due to increasing mechanical advantage as the centralizer's arm angle decreases in the smaller casing ID, the resulting centralizing force is very small. For example, FIG. 13B graphs the centralizing force relative to inner casing diameters for the conventional type of centralizer assembly. As seen here, the centralizing force dips below a required force and allows the tool to be eccentric in the casing.

(51) In contrast to the conventional biasing arrangement, the disclosed biasing arrangement offers two-stage biasing. For example, FIG. 14A graphs spring force relative to inner casing diameters for the biasing arrangement of the present disclosure. A first stage applies to larger casing sizes (e.g., about 5.2-in and above), both springs 60a-b are engaged, and the effective spring constant is low. In a second stage at small casing sizes (e.g., below about 5.2-in), only one spring 60a (with a higher spring constant) is engaged, making the spring constant high. Thus, the first stage produces a low spring constant with low mechanical advantage, and the second stage provides a high spring constant with high mechanical advantage. These act to level out the centralizer's side force profile over the entire range of casing sizes for which the centralizers (50a-b) are intended.

(52) In particular, FIG. 14B graphs centralizing force relative to inner casing diameters for the biasing arrangement of the present disclosure. As noted above, there is a minimum requirement for the centralizing force of the centralizer to keep the tool centered. The resulting centralizing forces in the two stages give the centralizer an overall centralizing force above the minimum requirement.

(53) The foregoing description of preferred and other embodiments is not intended to limit or restrict the scope or applicability of the inventive concepts conceived of by the Applicants. It will be appreciated with the benefit of the present disclosure that features described above in accordance with any embodiment or aspect of the disclosed subject matter can be utilized, either alone or in combination, with any other described feature, in any other embodiment or aspect of the disclosed subject matter.

(54) In exchange for disclosing the inventive concepts contained herein, the Applicants desire all patent rights afforded by the appended claims. Therefore, it is intended that the appended claims include all modifications and alterations to the full extent that they come within the scope of the following claims or the equivalents thereof.